`DatabaseDescriptor#clientInitialization` should set the `newFailureDetector` (maybe to a NoOpFailureDetector?)

With the introduction of a configurable FailureDetector, client users of the cassandra-all jar now need to call not just `clientInitialization` but also `setDefaultFailureDetector` in order to avoid an NPE when the failure detector is constructed. This is a breaking change from previous versions where this was not necessary.

Calls to DatabaseDescriptor#clientInitialization should set newFailureDetector to something, either by calling setDefaultFailureDetector or creating a different (NoOp?) FailureDetector.